JP2714065B2 - Refrigeration cycle for low temperature - Google Patents

Description

The present invention relates to a low-temperature refrigeration cycle using a non-azeotropic refrigerant mixture, which is suitable for preventing a rise in temperature of refrigerant discharged from a compressor. It relates to a refrigeration cycle.

[Conventional technology]

A conventional apparatus extracts a refrigerant from an intermediate portion of a condenser in a refrigeration cycle in which a non-azeotropic mixed refrigerant is sealed as described in JP-A-59-217458, and the refrigerant is introduced into a compression chamber of a compressor. When the refrigerant that has been injected and liquefied evaporates, heat is taken from the compressor to cool the compressor.

[Problems to be solved by the invention]

In the above prior art, the liquid refrigerant supply pipe to the compression chamber of the compressor is taken from a branch pipe branched from the middle of the condenser.
In this case, the non-azeotropic mixed refrigerant that has flowed into the condenser is usually cooled while flowing in the heat transfer tube, and mainly the low-pressure refrigerant is liquefied, and the liquid refrigerant and the refrigerant in the gas state having a large ratio of the high-pressure refrigerant coexisted. The state is a so-called two-phase flow state,
Since the liquid and gas flow in a two-phase state is a complicated flow, the liquid refrigerant cannot be stably supplied to the compression chamber. In particular, when there is a change in the condenser load such as a change in the temperature of the cooling water or air serving as the cooling medium of the condenser, the refrigerant liquefaction amount is reduced, and the refrigerant may be in a state of a large gas refrigerant ratio. In such a state, the amount of the liquid refrigerant supplied to the compression chamber is reduced, which causes an increase in the temperature of the discharge gas, and the cooling effect of the compressor is deteriorated.

In addition, reciprocating or rotary type compressors are also conceivable as refrigerating cycle compressors, but in these compressors, as is well known, fluctuations in pressure applied to a communication hole provided for liquid injection into a compression chamber are known. large. It is also conceivable that liquid compression occurs. Therefore, it is difficult for a reciprocating compressor or a rotary compressor to perform stable liquid injection, and there is a problem in terms of reliability. That is, if the pressure difference between the liquid refrigerant outlet for the liquid injection and the pressure in the compression chamber is large, the amount of liquid injection also fluctuates, and the amount of refrigerant flowing through the main circuit also fluctuates. As a result, especially in the case of a low-temperature cycle using a non-azeotropic refrigerant mixture, the ratio of refrigerant in each part of the cycle changes, resulting in an unstable operation state. Further, in a cycle using a reciprocating compressor, when liquid flows into the compression chamber, the risk of breaking the discharge valve increases.

An object of the present invention is to provide a liquid refrigerant to a compression chamber of a compressor in a low-temperature refrigeration cycle using a non-azeotropic mixed refrigerant. It is an object of the present invention to provide a low-temperature refrigeration cycle with high reliability in which a stable operating state can be obtained.

[Means for solving the problem]

To achieve the above object, the present invention uses a non-azeotropic mixed refrigerant, comprising a compressor, an evaporator, a plurality of condensers, a plurality of expansion devices, and a plurality of refrigerant separators. In a low-temperature refrigeration cycle for sequentially condensing the condensed liquid in each of a plurality of condensers and separating the condensed liquid by a refrigerant separator, and supplying the condensed liquid to an evaporator, a scroll compressor used as a compressor, Take out liquid refrigerants with different temperatures from the middle of each of the liquid pipes connecting the expansion device,
And a liquid injection pipe communicating with the scroll compressor.

By using a scroll compressor as the compressor, fluctuations in pressure applied to the liquid injection hole, fluctuations in the pressure of the liquid injection outlet and the pressure difference in the compression chamber can be reduced. Furthermore, since the liquid refrigerant for liquid injection is taken out as a liquid refrigerant having a different temperature from the middle of each of the plurality of liquid pipes, the temperature of the cooling medium changes due to air or water in the condenser on the upstream side, and the load on the condenser is reduced. Changes, and the amount of refrigerant liquefied in this condenser is reduced, the refrigerant that could not be liquefied in the upstream condenser in the further downstream condenser is also liquefied and supplied to the compression chamber of the scroll compressor. .

Therefore, the pressure serving as a driving force for liquid injection is stabilized, and a sufficient liquid refrigerant for liquid injection is secured even if the load on the condenser changes, preventing the discharge gas temperature from rising and preventing the compressor from operating. Cooling can be performed well.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The cycle of FIG. 1 includes a compressor 1, a condenser 2, a first cascade condenser 3, a second cascade condenser 4, an evaporator 5, an I-expansion device 6, a II-expansion device 7, and a III-expansion device 8. , The first refrigerant separator 9,
Main component devices such as the second refrigerant separator 10 are connected by piping. It is assumed that three types of non-azeotropic mixed refrigerants are enclosed in the cycle. The operation of the cycle will be described below.

The non-azeotropic mixed refrigerant sucked into the compressor is compressed here to become a high-temperature and high-pressure refrigerant gas and flows into the condenser 2. In the condenser 2, of the three types of non-azeotropic refrigerants, mainly high-boiling refrigerants are condensed and liquefied by being cooled by a cooling medium such as water or air. Most of the medium-boiling refrigerant and the low-boiling refrigerant flow out of the condenser 2 in a gaseous state. That is, the refrigerant is in a gas-liquid two-phase state in the condenser 2. The gas-liquid two-phase mixed refrigerant that has exited the condenser 2 then enters the I-th refrigerant separator 9,
Here, gas-liquid separation is performed. Gas-liquid separated medium boiling point refrigerant,
The mixed gas refrigerant having a large low boiling point refrigerant ratio is supplied to the refrigerant separator 9.
And flows into the high pressure side of the first cascade condenser 3 through the gas pipe 14. On the other hand, the liquid refrigerant separated by the I-th cooling separator 9 passes through the liquid pipe 12 and is hydraulically compressed by the I-expansion device 6, and then joins with the refrigerant flowing out from the low-pressure side of the second cascade condenser 4. Flows into the low pressure side of the I-cascade condenser 3,
It is used as a cooling heat source for the mixed gas refrigerant flowing into the high pressure side of the first cascade condenser 3 through the gas pipe 14. In the first cascade condenser 3, the intermediate boiling point refrigerant is mainly condensed and liquefied, and the refrigerant in a gas-liquid two-phase state flows out from the high pressure side of the first cascade condenser 3.
Flow into 10. Here, the gas-liquid two-phase refrigerant is separated into gas and liquid.
The gas refrigerant having a high ratio of the low-boiling refrigerant separated from the gas flows into the high-pressure side of the second cascade condenser 4 through the gas pipe 15. On the other hand, the liquid refrigerant separated by the second refrigerant separator 10 is
After the pressure is reduced by the second expansion device 7 through the liquid pipe 13, the refrigerant is combined with the refrigerant flowing out of the evaporator 5, and then the second cascade condenser 4 is cooled.
And is used as a cooling heat source for the mixed gas refrigerant flowing into the high pressure side of the second cascade condenser 4 through the gas pipe 15. The refrigerant having a high low boiling point refrigerant ratio that has been cooled and liquefied by the second cascade condenser 4 is decompressed by the third expansion device 8, and then flows into the evaporator. Here, a low temperature is generated. The refrigerant flowing out of the evaporator merges with the refrigerant depressurized by the second expansion device and the first expansion device as described above, and is used as a cooling heat source of the second cascade condenser and the first cascade condenser. Inhaled by the machine. If the temperature of the gas refrigerant discharged from the compressor becomes abnormally high while the above-described operation is performed, the liquid refrigerant may flow from the middle of one or both of the liquid pipes 12 and 13. And the refrigerant gas in the compression chamber is cooled by the liquid refrigerant which has been injected into the compression chamber of the compressor via the liquid injection pipe 19, so that the discharge gas temperature can be kept low. it can. That is, as described above, the liquid pipe 12 and the liquid pipe 13 are configured such that the liquid injection can be performed from two places, so that the temperature of the cooling medium (air or water) of the condenser 2 increases with the rise of the temperature of the condenser 2. When the amount of condensed and liquefied liquid decreases and the amount of branch liquid from the liquid pipe 12 cannot be secured sufficiently, the liquid refrigerant can also be branched from the liquid pipe 13 and liquid injection can be performed. Can be. In addition, by using a scroll type compressor having a characteristic that the pressure applied to the liquid injection hole communicating with the compression chamber is small, the pressure difference between the refrigerant outlet for the liquid injection and the compression chamber is reduced. Therefore, the flow rate of the liquid injection branched from the liquid pipe 12 and the liquid pipe 13 and the amount of refrigerant in the main circuit flowing through the I-expansion device 6 and the II-expansion device 7 are stable, and the refrigerant mixing in each part of the cycle is stabilized. The ratio becomes constant. As a result, fluctuations in the operating pressure of the cycle and the temperature of each part of the cycle due to a change in the refrigerant mixing ratio are reduced, and stable operation is obtained. Note that the valves 16 and 17 are valves for switching the location for taking out the liquid-injection refrigerant or for adjusting the liquid-injection amount.However, these valves may be eliminated so that the liquid-injection is always performed. Alternatively, a resistor such as a capillary tube may be used to appropriately distribute the liquid injection amount from the liquid pipes 12 and 13. In addition, one of the valves 16 and 17 is removed to perform liquid injection at all times, and the same effect as described above can be obtained even if liquid injection can be performed from the other side as necessary. .

The cycle shown in FIGS. 2 and 3 is different from the embodiment of the cycle shown in FIG. 1 in that a cascade condenser, a refrigerant separator,
Each inflator has a cycle configuration of one more. Since the operation principle and the like are not different from the cycle shown in FIG. 1, detailed description of the cycle shown in FIG. 2 and FIG. 3 is omitted. The cycle shown in FIG. 3 differs from the cycle shown in FIG. 2 in that the refrigerant for the liquid injection is taken from the liquid pipe 23 instead of the liquid pipe 13. However, liquid piping
The above-described effect can be obtained even from three places of the liquid pipe 13, the liquid pipe 13, and the liquid pipe 23.

When the scroll compressor used in the cycle described in FIGS. 1 to 3 is a so-called high-pressure chamber-type scroll compressor in which the internal space of the compressor chamber is a gas refrigerant discharged from the compression chamber. Since the motor coil for the compressor is in contact with the discharge gas refrigerant (the motor coil is cooled by the discharge gas), if the liquid injection effect is stably obtained as described above, the motor coil also cools. Since it is performed stably, it is possible to prevent the compressor from burning due to overheating of the motor coil. Also, if the cycle is not sufficiently cooled at startup or after startup, the high pressure refrigerant will not be liquefied, so the discharge pressure will increase and the discharge gas temperature will increase. If used, the discharge pressure (high-pressure side pressure) can be kept relatively low because the volume on the high pressure side of the cycle becomes large, so that the discharge gas temperature can also be lowered.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, even if the load of a condenser changes, a sufficient liquid-injection refrigerant can be stably supplied to a compression chamber, so that the discharge gas temperature can be increased and the compressor motor coil can be cooled well and can be performed stably. The obtained cycle operation state is obtained.

[Brief description of the drawings]

1, 2 and 3 are system diagrams each showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Condenser, 3 ... I Cascade condenser, 4 ... II Cascade condenser, 5 ... Evaporator, 6
…… I expansion device, 7 …… II expansion device, 8 …… III
Expansion device, 9 ... I refrigerant separator, 10 ... II refrigerant separator, 11 ... Expansion tank, 18 ... Valve, 19 ... Liquid injection pipe, 21 ... III expansion device, 22 ... Third refrigerant separator.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Naoto Katsumata, Inventor 390 Muramatsu, Shimizu-shi, Shizuoka Pref. Inside Shimizu Plant, Hitachi, Ltd. (56) References JP-A-55-72764

Claims (1)

(57) [Claims] 1. A compressor, an evaporator, a non-azeotropic refrigerant mixture,
It has multiple condensers, multiple expansion devices, and multiple refrigerant separators.The non-azeotropic mixed refrigerant is sequentially condensed in each of the multiple condensers, and the condensed liquid is separated by the refrigerant separator and supplied to the evaporator. In a low-temperature refrigeration cycle, a scroll compressor used as the compressor, and liquid refrigerants having different temperatures are taken out of the liquid pipes connecting the plurality of refrigerant separators and the expansion device, and the scroll is taken out. And a liquid injection pipe communicating with the compressor.